What is that red hammer icon?

I noticed a red hammer icon when viewing armor or weapons in the inventory. Can anyone explain what it means? What's the meaning of the number next to it?

The following screenshot shows the red hammer icon in the lower left area.

This means that some of your armor parts are (partially) broken and need to be repaired.

The first number (white, 30) indicates your armor value. In your case your character's armor would have a value of 30.

The second number (red, -1) shows you that your armor is broken and how much you lose of that value. So in your case the broken armor reduces your overall armor by 1, so that you have 29 armor.

This can also happen with just picked-up armor. So even if it's a new one, it can be (partially) broken.